A concerted action of a paired-type homeobox gene, aristaless, and a homolog of Hox11/tlx homeobox gene, clawless, is essential for the distal tip development of the Drosophila leg.
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The subdivision of the developing field by region-specific expression of genes encoding transcription factors is an essential step during appendage development in arthropod and vertebrates. In Drosophila leg development, the distal-most region (pretarsus) is specified by the expression of homeobox genes, aristaless and Lim1, and its immediate neighbor (distal tarsus) is specified by the expression of a pair of Bar homeobox genes. Here, we show that one additional gene, clawless, which is a homolog of vertebrate Hox11/tlx homeobox gene family and formerly known as C15, is specifically expressed in the pretarsus and cooperatively acts with aristaless to repress Bar and possibly to activate Lim1. Similar to aristaless, the maximal expression of clawless requires Lim1 and its co-factor, Chip. Bar attenuates aristaless and clawless expression through Lim1 repression. Aristaless and Clawless proteins form a complex capable of binding to specific DNA targets, which cannot be well recognized solely by Aristaless or Clawless. (+info)
Evaluation of the quality of porcine somatic cell nuclear transfer embryo by gene transcription profiles.
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This study aimed to evaluate the quality of porcine somatic cell nuclear transfer (SCNT) embryos by examining its gene transcription patterns. Embryos were produced by SCNT, intracytoplasmic sperm injection (ICSI) or under different conditions, and transcripts of genes for fibroblast growth factor receptor (FGFr) 2IIIc, FGFr72IIIb, X inactive-specific transcript (Xist), interleukin 6 (IL6), IL6 receptor (IL6r) alpha and c-kit ligand, were detected by real-time RT-PCR. The percentages of embryos in which these transcripts were detected were similar in SCNT and ICSI embryos. On the other hand, the transcriptional levels of the FGFr72IIIb and IL6ralpha genes were 0.5 times less and 2 times more, respectively, in SCNT blastocysts than those of ICSI blastocysts (p<0.05). When nuclear transfer was performed before or after activation of oocytes, embryos in the latter case showed significantly lower frequencies of having FGFr72IIIb (74% vs. 90%) and Xist (3% vs. 33%) transcripts compared to the former case embryos (p<0.05). When two lines of nuclear donor cells with different developmental potencies were used, the transcriptional profiles in the reconstructed embryos did not show any significant differences. Our study suggests that expression profiles of FGFr72IIIb, IL6ralpha, and Xist can be used as markers for the diagnosis of the developmental potency of porcine nuclear transfer embryos. (+info)
Growth factor regulation of lens development.
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Lens arises from ectoderm situated next to the optic vesicles. By thickening and invaginating, the ectoderm forms the lens vesicle. Growth factors are key regulators of cell fate and behavior. Current evidence indicates that FGFs and BMPs are required to induce lens differentiation from ectoderm. In the lens vesicle, posterior cells elongate to form the primary fibers whereas anterior cells differentiate into epithelial cells. The divergent fates of these embryonic cells give the lens its distinctive polarity. There is now compelling evidence that, at least in mammals, FGF is required to initiate fiber differentiation and that progression of this complex process depends on the synchronized and integrated action of a number of distinct growth factor-induced signaling pathways. It is also proposed that an antero-posterior gradient of FGF stimulation in the mammalian eye ensures that the lens attains and maintains its polarity and growth patterns. Less is known about differentiation of the lens epithelium; however, recent studies point to a role for Wnt signaling. Multiple Wnts and their receptors are expressed in the lens epithelium, and mice with impaired Wnt signaling have a deficient epithelium. Recent studies also indicate that other families of molecules, that can modulate growth factor signaling, have a role in regulating the ordered growth and differentiation of the lens. (+info)
JNK signaling pathway required for wound healing in regenerating Drosophila wing imaginal discs.
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We have examined wound healing during regeneration of Drosophila wing imaginal discs fragments by confocal microscopy and assessed the role of components of the JNK pathway in this process. After cutting, columnar and peripodial epithelia cells at the wound edge start to close the wound through formation and contraction of an actin cable. This is followed by a zipping process through filopodial protrusions from both epithelia knitting the wound edges from proximal to distal areas of the disc. Activation of the JNK pathway is involved in such process. puckered (puc) expression is induced in several rows of cells at the edge of the wound, whereas absence of JNK pathway activity brought about by hemipterous, basket, and Dfos mutants impair wound healing. These defects are accompanied by lowered or loss of expression of puc. In support of a role of puc in wound healing, hep mutant phenotypes are rescued by reducing puc function, whereas overexpression of puc inhibits wound healing. Altogether, these results demonstrate a role for the JNK pathway in imaginal disc wound healing, similar to that reported for other healing processes such as embryonic dorsal closure, thoracic closure, and adult epithelial wound healing in Drosophila. Differences with such processes are also highlighted. (+info)
Distinct populations of endoderm cells converge to generate the embryonic liver bud and ventral foregut tissues.
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The location and movement of mammalian gut tissue progenitors, prior to the expression of tissue-specific genes, has been unknown, but this knowledge is essential to identify transitions that lead to cell type specification. To address this, we used vital dyes to label exposed anterior endoderm cells of early somite stage mouse embryos, cultured the embryos into the tissue bud phase of development, and determined the tissue fate of the dye labeled cells. This approach was performed at three embryonic stages that are prior to, or coincident with, foregut tissue patterning (1-3 somites, 4-6 somites, and 7-10 somites). Short-term labeling experiments tracked the movement of tissue progenitor cells during foregut closure. Surprisingly, we found that two distinct types of endoderm-progenitor cells, lateral and medial, arising from three spatially separated embryonic domains, converge to generate the epithelial cells of the liver bud. Whereas the lateral endoderm-progenitors give rise to descendants that are constrained in tissue fate and position along the anterior-posterior axis of the gut, the medial gut endoderm-progenitors give rise to descendants that stream along the anterior-posterior axis at the ventral midline and contribute to multiple gut tissues. The fate map reveals extensive morphogenetic movement of progenitors prior to tissue specification, it permits a detailed analysis of endoderm tissue patterning, and it illustrates that diverse progenitor domains can give rise to individual tissue cell types. (+info)
Echinoid is a component of adherens junctions that cooperates with DE-Cadherin to mediate cell adhesion.
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Echinoid is an immunoglobulin domain-containing transmembrane protein that modulates cell-cell signaling by Notch and the EGF receptors. We show that, in the Drosophila wing disc epithelium, Echinoid is a component of adherens junctions that cooperates with DE-Cadherin in cell adhesion. Echinoid and beta-catenin (a DE-Cadherin interacting protein) each possess a C-terminal PDZ domain binding motif that binds to Bazooka/PAR-3; these motifs redundantly position Bazooka to adherens junctions. Echinoid also links to actin filaments by binding to Canoe/AF-6/afadin. Moreover, interfaces between Echinoid- and Echinoid+ cells, like those between DE-Cadherin- and DE-Cadherin+ cells, are deficient in adherens junctions and form actin cables. These characteristics probably facilitate the strong sorting behavior of cells that lack either of these cell-adhesion molecules. Finally, cells lacking either Echinoid or DE-Cadherin accumulate a high density of the reciprocal protein, further suggesting that Echinoid and DE-Cadherin play similar and complementary roles in cell adhesion. (+info)
Control of cell proliferation in the Drosophila eye by Notch signaling.
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Cell proliferation in animals must be precisely controlled, but the signaling mechanisms that regulate the cell cycle are not well characterized. A regulated terminal mitosis, called the second mitotic wave (SMW), occurs during Drosophila eye development, providing a model for the genetic analysis of proliferation control. We report a cell cycle checkpoint at the G1-S transition that initiates the SMW, and we demonstrate that Notch signaling is required for cells to overcome this checkpoint. Notch triggers the onset of proliferation by multiple pathways, including the activation of dE2F1, a member of the E2F transcription factor family. Delta to Notch signaling derepresses the inhibition of dE2F1 by RBF, and Delta expression depends on the secreted proteins Hedgehog and Dpp. Notch is also required for the expression of Cyclin A in the SMW. (+info)
Dlx2 over-expression regulates cell adhesion and mesenchymal condensation in ectomesenchyme.
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The Dlx family of homeodomain transcription factors have diverse roles in development including craniofacial morphogenesis and consists of 6 members with overlapping expression patterns. Dlx2 is expressed within the developing branchial arches in both the epithelium and mesenchyme and targeted deletion in mice has revealed roles in patterning and development of the craniofacial skeleton. Defects in Dlx2 null mice include skeletal anomalies of proximal branchial arch 1 derivatives while distal elements are largely spared indicating redundancy within the Dlx family. We have investigated the function of Dlx2 using in ovo electroporation and cell culture. Ectopic expression of Dlx2 within the neural tube beginning prior to emigration of neural crest cells at E1.25 drastically inhibits the migration of transfected cells and induces aggregation of transfected neuroepithelial cells within the neural tube at 24 h post-electroporation. By 48 h post-electroporation, the majority of transfected cells formed multicellular aggregates that were found adjacent to the basal side of the neural tube and very few Dlx2 expressing cells migrated to the level of the branchial arches. Similar results were obtained for Dlx5, suggesting these effects may be common to Dlx genes. Electroporation of the Dlx2 expression construct into branchial arch mesenchyme induced N-cadherin and NCAM, a dramatic increase in cell-cell adhesion relative to controls, and resulted in an increase in mesenchymal condensation. These results suggest a role for Dlx genes in regulating ectomesenchymal cell adhesion and supports the possibility that the skeletal dysmorphology seen in Dlx null mice may derive from abnormalities at the condensation stage. (+info)